The present invention relates to a speed gear having a speed gear section and a clutch spline section mainly used for a transmission gearbox, and a manufacturing method and apparatus for the speed gear.
Conventionally, a speed gear having a speed gear section and a clutch spline section used for a transmission gearbox is manufactured by methods such as:
1. A method which comprises forming a speed gear section and spline teeth respectively by submitting a speed gear section and a clutch spline section, integrally molded by hot forging, to machining such as hobbing, etc;
2. A method which comprises forming a speed gear section by submitting a speed gear section molded by hot forging to machining such as hobbing, etc., and integrating the speed gear section and a clutch spline section having spline teeth molded by cold forging by either spline connection or electron beam welding; and
3. A method which comprises forming a speed gear section by submitting a speed gear section and a clutch spline section integrally molded by hot forging to machining such as hobbing, etc. and forming a clutch spline section by hot forging and cold forging, respectively.
By the way, methods 1 to 3 all consist in forming the speed gear section by submitting the speed gear section to machining such as hobbing, etc. For that reason, they had a problem in that the metal flow of the section of speed gear was cut off, not only reducing the strength of the gear but also inevitably leading to an increase of the manufacturing cost due to machining.
As a solution to this problem, adoption of a method for forming speed gear teeth in the speed gear section by cold forging with a press may be conceivable, but no high-accuracy speed gear section could be manufactured because of the difficulty of securing concentricity between the clutch spline section and the speed gear section forming speed gear teeth.
Moreover, a speed gear W generally used for the transmission gearbox at present is provided, as shown in FIG. 11, with speed gear section Pa and clutch spline section Pb, forming helical teeth Ga as speed gear teeth at the speed gear section Pa and an involute spline with a back taper Gb having a chamfer Cb at the tip of the clutch spline section Pb, respectively.
The helical teeth Ga formed at the speed gear section Pa generally have, as shown in FIG. 10 (C), a torsional angle xcex1 of 15xc2x0 to 35xc2x0 on the right or on the left, and are formed as high teeth to reduce the gear noise produced during high-speed rotation of the speed gear W.
For that reason, in the case where an attempt is made to form helical teeth Ga by cold forging with a press, for example, the greater part of the forming pressure must be supported by the tooth flank Fa of the helical teeth Ga. This causes deflection of the helical teeth Ga, producing a gap in the tooth flank Fb and inducing the material to flow into that gap.
As a result, the helical teeth Ga are formed differently at the torsional angle xcex1 of the tooth flank Fa and the torsional angle xcex1 b of the tooth flank Fb, making it difficult to manufacture a speed gear of high accuracy. In addition, since this trend becomes particularly conspicuous as the torsional angle a gets larger, it was impossible to form helical teeth Ga with a torsional angle a of 30xc2x0 or more by cold forging with a press.
Furthermore, as the speed gear W, a type forming helical teeth Ga having crowning Ca on the tooth flank (see FIG. 10 (D)) at the speed gear section Pa was also adopted. But this crowning could not be formed by cold forging with a press.
In view of the problems inherent in conventional speed gears and their manufacturing methods, the object of the present invention is to provide a speed gear having a speed gear section and a clutch spline section including speed gear teeth and an involute spline with a back taper having a chamfer at the tip, and a manufacturing method and apparatus for the speed gear.
To achieve the objective, the speed gear according to the present invention has a speed gear section and a clutch spline section integrally formed by forging. The clutch spline section is provided with an involute spline with a back taper having a chamfer at the tip. Speed gear teeth are formed by forging with rolling dies at the speed gear section with reference to the clutch spline section forming the involute spline with a back taper.
The speed gear forming the subject of the present invention includes a speed gear having helical teeth or flat teeth as the teeth of the speed gear.
Moreover, the speed gear forming the subject of the present invention also includes a speed gear having crowning on the tooth flank.
Furthermore, the speed gear forming the subject of the present invention further includes a speed gear in which the tip diameter of the back tapered involute spline formed on the clutch spline section is larger than the root diameter of the speed gear teeth formed on the speed gear section and the clearance between the speed gear section and the clutch spline section is no more than 2 mm.
Further, the speed gear forming the subject of the present invention includes a speed gear in which an involute spline with a back taper is formed in a shape conformable to the tip shape of dies by pushing in the dies, radially disposed against the axial line of the gear among spline teeth parallel to the axial line of the gear formed by forging, toward the center of gear in a direction perpendicular to the axial line of the gear.
The manufacturing method of the speed gear according to the present invention comprises integral molding, by either hot or warm forging, the speed gear section and the clutch spline section, rough-forming speed gear teeth in the speed gear section and involute splines parallel to the axial line of the gear in the clutch spline section, forming the involute splines parallel to the axial line of the gear formed on the clutch spline section by cold forging into an involute spline with a back taper having a chamfer at the tip, and then finish forming the speed gear teeth formed at the speed gear section. The finish forming of the speed gear teeth is done by forming the speed gear teeth by rolling dies, by cold forging, while turning them around a shaft hole located with reference to the clutch spline section forming the involute spline with a back taper.
In this case, the manufacturing method may be constructed in a way to form crowning on the tooth flank of the speed gear teeth by means of rolling dies.
Moreover, the forming of an involute spline with a back taper may be performed by pushing in dies, radially disposed against the axial line of the gear among spline teeth parallel to the axial line of the gear formed at the clutch spline section, toward the center of the gear in the direction perpendicular to the axial line of the gear, in a shape conformable to the tip shape of the dies.
The manufacturing apparatus of the speed gear according to the present invention, relating to the method of the present invention, comprises a chuck for holding the shaft hole at the center of the work gear, a tail stock for turning the work gear through the chuck around its shaft hole, a synchronizing gear disposed in the tail stock that turns together with the tail stock, a driven gear engaging with the synchronizing gear, and a rolling spindle on which are disclosed rolling dies. The work gear is submitted to finish forming of the rough-formed speed gear teeth by the rolling dies turning in synchronization with the work gear while turning the work gear around its shaft hole through the synchronizing gear and the driven gear.
In this case, the chuck may comprise a collet chuck and a male cone to be inserted in the collet chuck so as to expand the diameter of the collet chuck and hold the shaft hole at the center of the work gear.
Moreover, the rolling dies may be constructed to perform finish forming of helical rough-formed teeth.
Furthermore, the rolling dies may be constructed to also perform crowning at the tooth flank of the rough-formed speed gear teeth.
According to the present invention, it becomes possible to integrally form, by forging, the speed gear section and the clutch spline section including speed gear teeth and an involute spline with a back taper having a chamfer at the tip, thus providing the following actions and effects.
1. By forming speed change gear teeth and an involute spline with a back taper having a chamfer at the tip by forging, it becomes possible to improve the strength of the gear without cutting the metal flow of the teeth, avoiding an increase in manufacturing cost due to machining, and reducing the manufacturing cost of the speed gear.
2. It is easy to concentrically secure the clutch spline section forming an involute spline with a back taper with the speed gear section forming speed gear teeth, enabling the manufacture of a highly-accurate speed gear.
3. When forming helical teeth as speed gear teeth, it is possible to manufacture a highly-accurate speed gear, especially helical teeth with a torsional angle of 30xc2x0 or more, by forging.
4. When forming speed gear teeth by forging, it is possible to also perform crowning at the tooth flank of the speed gear teeth at the same time.
5. By forming an involute spline with a back taper having a chamfer at the tip by forging, it becomes possible to not only manufacture a highly-accurate speed gear without hooking due to machining, but to also obtain a speed gear with excellent shift feeling.
6. The absence of restrictions on the component materials of the speed gear enables the use of high-strength, difficult to cut steel, making it possible to manufacture a compact speed gear easily.
7. It is possible to manufacture a speed gear with a shape difficult to achieve through machining, and obtain a compact speed gear.